INTERNATIONAL TELECOMMUNICATION UNION HANDBOOK SELECTION AND USE OF PRECISE FREQUENCY AND TIME SYSTEMS HANDBOOK SELECTION AND USE OF PRECISE FREQUENCY AND TIME SYSTEMS 1997 AND USE OF PRECISE FREQUENCY HANDBOOK SELECTION *10504* Printed in Switzerland Geneva, 1997 ISBN 92-61-06511-2 ADIOCOMMUNICATION UREAU THE RADIOCOMMUNICATION SECTOR OF THE ITU The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency spectrum by all radiocommunication services, including satellite services and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are performed by World and Regional Radiocommunication Conferences and Radiocommunication Assemblies supported by Study Groups. Contact address for inquiries about radiocommunication matters: ITU Radiocommunication Bureau Place des Nations CH-1211 Geneva 20 Switzerland Telephone +41 22 730 5800 Fax +41 22 730 5785 Internet [email protected] X.400 S=brmail; P=itu; A=400net; C=ch Contact address for orders of ITU publications: ITU Sales and Marketing Service Place des Nations CH-1211 Geneva 20 Switzerland Telephone +41 22 730 6141 English Telephone +41 22 730 6142 French Telephone +41 22 730 6143 Spanish Fax +41 22 730 5194 Telex 421 000 uit ch Telegram ITU GENEVE Internet [email protected] X.400 S=sales; P=itu; A=400net; C=ch © ITU 1997 All rights reserved. No part of this publication may be reproduced or utilised in any form or by any means, electronic or mechanical, including photocopying and microfilm, without written permission from the ITU. INTERNATIONAL TELECOMMUNICATION UNION HANDBOOK SELECTION AND USE OF PRECISE FREQUENCY AND TIME SYSTEMS 1997 RADIOCOMMUNICATION BUREAU © ITU 1997 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without written permission from the ITU. - iii - PREFACE This Handbook on the Selection and Use of Precise Frequency and Time Systems has been developed by the Group of the Experts in the field of frequency standards and time signals of Radiocommunication Study Group 7 – Science Services under the Chairmanship of Mr. R. Sydnor (Editor, USA) and Mr. David W. Allan (Assistant Editor, USA). This Handbook consists of 10 Chapters which describe basic concepts, frequency and time sources, measurement techniques, characteristics of various frequency standards, operational experience, problems and future prospects. The contents include detailed explanations and many references that can be consulted for additional details. The technical content of this Handbook is intended for the use by administrations of both developing and developed countries and by the Radiocommunication Bureau. The Handbook will also be useful to engineers of the scientific and industrial organizations. Robert W. Jones Director, Radiocommunication Bureau - iv - Introduction by Radiocommunication Study Group 7 Chairman The Radiocommunication Study Group for the Science Services (SG-7) was created through a structural reorganisation in 1990 at the Dusseldorf CCIR Plenary Assembly. At that time, the Space Research and Radio Astronomy Study Group (SG-2) was consolidated with the Time and Frequency Standards Study Group (SG-7) to form a new Study Group 7 on Science Services. Many of the activities in the Science Services SG are associated with advancing the state of the art in the use of the radio spectrum to achieve scientific objectives. In this regard, the time and frequency standards community has long been associated with the International Telecommunication Union with the express purpose of developing Recommendations for the use of the radio spectrum to facilitate the dissemination of precise time references and for standardising the methods for this dissemination. An essential corollary is the specification of precise frequency standards and the techniques for their implementation. While the development of Recommendations was, and continues to be, the principal focus of the Study Group activities, it has become clear that the experts who work on these matters in the Study Group have much basic information to offer to their scientific and lay colleagues who depend on precise time and frequency data for implementing a variety of communications techniques. These techniques include generation of official time for all nations, telecommunications, navigation (including collision avoidance), power systems, position determination and surveying, avionics, transportation systems, space exploration, astronomy and astrometry (especially millisecond pulsar measurements), earthquake monitoring, and all national standards laboratories. Thus it was decided to prepare and publish this Handbook so that all users of these standards could more completely understand precise time and frequency sources and systems in order to better design and apply these powerful tools. As Chairman of Study Group 7, it is my honour and pleasure to present this Handbook to the community of users of precise time and frequency standards who will, I am sure, find it an invaluable reference tool in their own work. H. G. Kimball Geneva 1996 - v - Acknowledgements We should like to thank the following administrations and organizations for their kind support and participation on the part of their experts: France, Germany (Federal Republic of), Italy, Switzerland (Confederation of), United States of America, Hewlett-Packard Laboratories (USA), Istituto Elettrotecnico Nazionale G. Ferrar (Italy), Jet Propulsion Laboratory (USA), Laboratoire de L'Horloge Atomique (France), National Institute of Standards and Technology (USA), Observatoire de Neuchâtel (Switzerland), Observatoire de Paris (France), Physikalische- Technische Bundesanstalt (Germany), Polytechnico di Torino (Italy) and Bureau international des poids et mesures (BIPM), and to acknowledge the contributions and the helpful guidance and discussions with the following personalities: Chapter 1 Claude Audoin Laboratoire de L'Horloge Atomique, France; Chapter 2A Andreas Bauch Physikalische-Technische Bundesanstalt, Germany; Chapter 2B Roger Beehler National Institute of Standards and Technology, USA; Chapter 3 Laurent-Guy Bernier Observatoire de Neuchâtel, Switzerland; Chapter 4 Fred Walls National Institute of Standards and Technology, USA; Chapter 5 Richard L. Sydnor Jet Propulsion Laboratory, USA; Chapter 6 Claudine Thomas Bureau international des poids et mesures, France; Chapter 7 Sigfrido Leschiutta Polytechnic di Totino, Italy; Franco Cordara Istituto Elettrotecnico Nazionale G. Ferrar, Italy; Chapter 8 Michel Granveaud Observatoire de Paris, France; Chapter 9 Leonard Cutler Hewlett-Packard Laboratories, USA; Chapter 10 Donald Sullivan National Institute of Standards and Technology, USA; and also to thank Messrs. R. L. Sydnor and D.W. Allan for their editorial work. - vi - Table of Contents Preface iii Introduction by Study Group 7 Chairman iv Acknowledgements v Introduction to the Handbook 1 Glossary 2 Chapter 1 Introduction and basic concepts 1.1 Historical sketch 11 1.2 Basic principles of frequency standards 12 1.2.1 Quartz crystal frequency standards 12 1.2.2 Atomic frequency standards 12 1.3 Basic metrological concepts 15 1.3.1 Frequency stability 15 1.3.2 Accuracy 18 1.3.3 Reproducibility, resettability 19 References 20 Chapter 2 Available frequency and time sources Overview of Chapter 2 23 Part A Local frequency and time sources 2.1 Introduction 24 2.2 Quartz crystal frequency standards 24 2.2.1 The resonator 24 2.2.2 The oscillator 25 2.3 The rubidium gas cell frequency standard 25 2.4 The hydrogen maser 27 2.5 The cæsium beam frequency standard 29 Part B Steering references 2.6 Introduction 33 2.7 Factors to be considered in the selection and use of alternative time-and-frequency dissemination services and techniques 33 2.8 Comparisons of alternative sources and dissemination techniques for precise time-and-frequency references 34 2.9 Additional information relating to the use of the various alternative services, systems, and techniques 34 References 46 Bibliography 47 Chapter 3 Characterisation: frequency domain, time domain 3.1 Introduction 51 3.2 Model of the oscillator 51 3.2.1 The phasor model and the analytic signal 51 3.2.2 The low-noise oscillator 51 3.2.3 Spectrum of the low-noise oscillator 52 3.2.4 The high-noise oscillator 53 3.2.5 Spectrum of the high-noise oscillator 53 3.2.6 Effect of frequency multiplication 53 3.2.7 Demodulation of the noise processes 54 - vii - 3.2.8 Standard definition of noise processes 54 3.2.9 Multiplicative and additive noise 55 3.2.10 Polynomial model 56 3.3 Characterisation: definitions and methods 57 3.3.1 Spectral domain 57 3.3.2 Time domain 58 3.3.3 Environmental 74 3.4 A bridge to the next Chapter 74 3.5 Appendix: Random processes 75 3.5.1 Introduction 75 3.5.2 Definition of a random process 75 3.5.3 Stationary random processes 75 3.5.4 Non-stationary random processes 75 3.5.5 Auto-correlation function 75 3.5.6 Power spectral density 75 3.5.7 Linear filtering of random processes 76 References 77 Chapter 4 Measurement techniques (Metrology) Introduction 81 4.1 Direct measurements of time (phase) and frequency 90 4.1.1 Direct measurements of time (phase) 90 4.1.2 Direct measurements of frequency 91 4.2 Heterodyne measurements of frequency and phase (time) 92 4.2.1 Heterodyne measurements of phase (time) 94 4.2.2 Heterodyne measurements